The following abbreviations and terms are herewith defined:                BS base station (e.g., any generic network access node)        C-RNTI cell radio network temporary identifier        D2D device-to-device        DL downlink        eNB base station in an LTE/LTE-A system        E-UTRAN evolved UTRAN        LTE long term evolution of UTRAN (also known as 3.9G)        LTE-A LTE advanced        OFDM orthogonal frequency division multiplex        PRB physical resource block        QoS quality of service        RRM radio resource management        SRS sounding reference signal        TTI transmission time interval        UE user equipment (e.g., mobile or subscriber station SS/MS, terminal)        UL uplink        UMTS universal mobile telecommunications system        UTRAN UMTS terrestrial radio access network        WiMAX worldwide interoperability for microwave access        
The future development of wireless communication systems are trending toward integrating network topologies rather than having multiple networks using different protocols overlying one another in the same geographic space. For example, there is some research in both industry and the academy into heterogeneous networks that are a deployment of macro, micro, pico, and/or femto cells and using relay nodes in the same LTE/LTE-A cellular overlay topology to all exploit the same radio spectrum. Another area of research in this integration concept is to allow direct communication between user devices when they are close to one another. This is often referred to as device-to-device D2D communications, and unlike cognitive radio which exploits spectrum ‘holes’ that go unused by the cellular scheduling entity, D2D communications use licensed radio spectrum that is specifically allocated by the cellular network. One likely implementation for D2D is within a ‘home’ cell. Proposals for D2D variously are within WiMAX, HiperLAN 2, and Tetra protocols, to name a few non-limiting examples.
D2D communication may also have characteristics of more general machine-to-machine (M2M) communication where machines communicate directly with each other under supervision of cellular network and sharing the radio resources with cellular users. D2D communication may provide efficient solutions also for local M2M communication schemes in the future. A typically assumption for D2D communications is that the D2D links utilize uplink UL radio resources of the cellular system controlled by the eNB/E-UTRAN.
A problem arises in power control for D2D communications in that different radio resource management RRM functions which are optimized with accurate power measurements or power control commands have different time latencies. Decisions by the cellular network as to what specific radio resources to allocate to the D2D links have a high latency and might be affected by power density available for those links. Communications on the D2D links themselves require more immediate power control so the D2D devices receive signals from the network and from the other D2D device(s) at a similar receive power level to avoid the near/far problem in code division multiplexed systems.
In traditional LTE systems, sounding reference signals (SRSs) are sent on the last SC-FDMA symbol in an UL subframe, if SRS is configured for the sending UE by higher layer signaling. The SRS can occupy a bandwidth different from that used for data transmission. UEs transmitting SRS in the same subframe can be multiplexed via either frequency or code division multiplexing. The subframes in which SRS are transmitted by any UE within the cell are indicated by cell-specific broadcast signaling. The eNB may either request or configure a UE to transmit SRS periodically until terminated. Specifically, in LTE there is a 1-bit UE-specific signaling parameter, ‘duration’, which indicates whether the requested SRS transmission is single or periodic. This of course is for cellular communication, not D2D which is not a part of LTE.
Relevant to D2D communications, one particular approach for power control is in a co-owned US patent application entitled “METHOD AND APPARATUS FOR PROVIDING INTERFERENCE MEASUREMENTS FOR DEVICE-TO-DEVICE COMMUNICATION” (Ser. No. 12/558,463, filed on Sep. 11, 2009). In that reference the base station determines the D2D pathloss or expected level of interference by requesting the devices to perform interference power measurements. Then the pathloss or interference estimates can be used for coordinating the D2D and cellular communication mode transmission on the same band. Examples include the eNB giving a list of C-RNTIs to the D2D devices which follow DL PDCCHs to find corresponding resources for the identifiers, and the D2D devices measure power density when they find a grant for certain resources with a listed identity. The eNB then finds the relevant scheduling restrictions and uses the information to suppress interference between the cellular and D2D communications. Another example finds the eNB providing a list of resources rather than the list of identifiers.
The non-limiting examples detailed below exhibit a more comprehensive power measurement and power control approach that is particularly useful for D2D communications, though of course not limited only to D2D links.